The Physics of a Skateboard
by Flaming Trails
Summary: Marty attempts to teach Doc how to skateboard, with less than optimal results.


The Physics of a Skateboard

by Flaming Trails

A Back To The Future: PreTime Story

Disclaimer: I don't own BTTF. If I did, we'd have some solid evidence on how Doc and Marty met.

_Notes: I wrote this in response to the backtothefanfic LiveJournal challenge, although the actual idea has been in my head a lot longer. Doc's physics lecture is half real science, half pseudo-science. Marty's "this is familiar" line refers to how he met Doc in "Best Friends Forever" -- he crashed into his garbage cans. The exchange about Doc's weight is adapted from the Part II draft script on bttf . com_

March 6th, 1984

Hill Valley

2:47 P.M.

Doc was straightening up his trash cans for the second time that week when he heard the familiar rattle of hard plastic wheels on concrete behind him. Smiling, he turned to see his best friend Marty McFly, skateboarding up to him. "Hi Marty."

"Hey Doc." Marty surveyed the dented cans. "They knock over the garbage cans again?"

"Yes, they did," Doc sighed. "I will never for the life of me understand why they think scattering trash all over my driveway is so funny." He paused. "Then again, I don't understand a lot of what they do."

"They're just idiots. Don't let it get ya down." Marty flipped his skateboard into his hand. "You mind helping me with my science homework?"

"Not at all," Doc said, leading Marty inside. Einstein, resting on Doc's cot, greeted them with a sleepy bark. "What seems to be the trouble?"

"Well, we're studying Newton's Laws of Motion at the moment," Marty explained, pulling his book and notebook out of his backpack. "I think I've got the idea, but I'm not sure if I did the problems right. It's complicated stuff."

"Oh, it isn't really."

"Maybe not to you," Marty retorted. "You're a genius. Nationally recognized and all that."

"No, Marty, I'm serious. This is the area of physics used most in everyday life. You probably just need a real world example to understand it fully." Doc's eyes darted around the garage, then came to rest at Marty's feet. "Take your skateboard."

"My skateboard?"

"It's a perfect example of rolling and sliding motion, not to mention friction." Doc picked up the skateboard and rolled it on the table. "See? When I apply a certain amount of force x, I cause instantaneous acceleration, calculated from the radius of the wheels, r, times alpha, previously defined. With a constant friction of f, previously defined, with the wheels rotating at a speed of y inches per second -- not the proper scientific measurements, but they'll do for this example -- the skateboard moves approximately three feet. Without the friction, of course, it would roll on forever -- or at least until it fell off the table or hit something."

Marty caught the skateboard as it rolled toward him. A sudden, sly grin appeared on his face. "You know a lot about the physics of this thing, don't ya?"

"Well, it was my main area of study in school."

"Yeah, I know. But -- could you ride one?"

Doc blinked. "Excuse me?"

Marty got up, still grinning. "Could you ride a skateboard, Doc?"

"Ah -- well -- they didn't have them when I was a teenager, so I really don't know. Theory and practice are two very different things."

"Come on, Doc, it's easy! I'll teach ya!" Marty grabbed Doc's sleeve and pulled him into the garage. "It's all just keeping your balance. Watch." Marty set the skateboard down, hopped on, and pushed off. He expertly glided around the garage, steering the board with his foot. "See? Nothing to it."

Doc had to admit, Marty did make it look very easy. Maybe he could ride a skateboard. Then again, Marty had been practicing for at least two years. "I'm still not sure," he said as Marty stopped in front of him.

"Relax Doc. I bet you'll be skateboarding like a pro in a hour." Marty hopped off the board. "Just put your left foot on it, steady it, then push off with your right. It's kinda like riding a bike, honestly."

"Something else I haven't done in ages," Doc muttered, putting his foot on the board anyway. He carefully steadied it, took a deep breath, and gave himself a quick push.

The board promptly rolled out from under his feet, sending him crashing to the floor. Marty dropped to his knees. "Doc! Jesus, you okay?"

"Fine. Just waiting for my vertebrae to realign." Doc winced. "Ouch. I'm going to feel that in the morning."

Marty helped him to his feet. "It's okay, Doc. I fell a lot at first too." He retrieved the skateboard from the driveway. "Try a slower push-off this time."

"All right." Doc steadied the board again with his left foot, then gradually pushed back with his right. The board obligingly rolled more slowly, allowing Doc to try and get both feet on the board. Unfortunately, he missed and fell off again, right into his DeLorean. The stainless steel was slightly more forgiving than the concrete, but not by much. "Great Scott," Doc moaned. "I hope I didn't damage the wiring."

"You fall on your DeLorean, and you're worried about it!"

"Well, it's a very sensitive project. I don't want anything happening to it." Doc examined the wires. "Thank God, they're fine."

Marty nodded, looking thoughtful. "Okay, this isn't working. Maybe I can be your crutch."

"Crutch? You mean, let me hang onto you?"

"Exactly. It'll help you keep your balance anyway."

"I"m not so sure about that. You're a lot smaller than I am."

"Come on, it's worth a try." Marty winked. "If you put your mind to it, you can accomplish anything."

Doc was seriously starting to regret ever saying that phrase to Marty. The teen had a tendency to use it to coerce him into doing things he didn't want to do. "All right, all right." He watched as Marty once again retrieved the skateboard and brought it over. "I just don't want you getting hurt as well."

"Trust me, Doc, we'll be fine." Marty waited for Doc to get on, then had him hold onto his shoulder. "Now remember, slow push-off."

"Right, I remember." Doc gripped Marty's shoulder tightly. "Let's hope third time's the charm." Taking a deep breath, he pushed off.

For a few minutes, Marty's idea seemed to work. Doc was able to get both feet on the board and keep his balance as they rolled into the driveway. Marty grinned at him. "See, what did I tell ya?"

Doc smiled back. "This is much better."

"Ready to let go and try it on your own?"

"Let me just turn around so we're not heading into the street. I don't think I'm quite ready for--"

There was a sudden burst of loud barking behind them. Doc's head jerked around to see Einstein, apparently finished with his nap, running at them at full throttle. With a thrill of horror, Doc remembered how much Einy loved to chase Marty on his skateboard. "Einstein, NO!"

It was too late. Barking joyfully, Einy leapt onto the skateboard, upsetting the fragile balance. Both Marty and Doc were thrown sideways. By sheer perverse fate, they fell right into Doc's garbage cans.

For a moment, there was silence as Einy mouthed his prize. Then Marty quipped, "Well, this feels familiar."

Doc sat up with a groan. "Thank you, Marty. I was afraid I wouldn't make my bruise quotient for the day."

Marty sat up too, rubbing his lower back. "Think that's enough for one day?"

"I think this has been enough for a month!" Doc slowly got to his feet. "I knew this was a bad idea! I knew that if something happened, I'd drag you down with me! I'm 211 pounds, you're--"

"You're 211 pounds?" Marty repeated, startled.

"It's all muscle, Marty."

"Like hell. At least half's Burger King, I'm sure."

"But the other half is all muscle," Doc grinned. That quickly dropped into a worried look. "Are you all right?"

"Fine, Doc, don't worry." Marty got up, watching Einy play with his skateboard. "Look, all you need is more practice. Anybody can pick up skateboarding."

As if to prove his point, Einy jumped on the board and rolled over to them. Doc glared at the dog. "Sure, it's easy for you," he muttered. "You have four legs."

Einy barked. Marty chuckled and knelt down to scratch behind his ears. "Hey, if he can do it, you can do it."

"That may be so, but I've lost any interest in doing it. That last fall was the last straw." Doc massaged his left arm. "I may not act my age, Marty, but I'm definitely not one of your teenage friends. Even if I did manage to learn how to skateboard, I'd really have no use for the skill."

"Yeah, I guess you're right," Marty conceded. "You should stick to talking physics."

"I fully intend to." Doc smiled a little. "But -- thanks anyway for trying to teach me."

"No problem, Doc."

Doc winked. "You know, if I didn't know you better, I'd swear you were trying to bump me off."

"Hey, I am named in your will. . . ."

A few minutes later, Jennifer was baffled to see Doc chasing Marty around his house, throwing garbage at him.

The End


End file.
